The invention disclosed herein relates generally to optomechanical switching, and more particularly to snap acting mechanical devices for achieving precision switching of light carried through optical fibers.
Use of mechanically switched light signals for performing monitoring and control functions and mechanical devices for achieving such switching have been in common use for some time. Systems using light signals have a number of well known advantages over electrical systems, such as offering intrinsic safety in explosive and other hazardous environments. In addition, mechanically actuated devices for switching light signals have a number of advantages over corresponding devices for switching electrical signals, such as immunity to contact bounce and wear. Apparatus for carrying and switching light signals also tends to be relatively immune to changes caused by environmental conditions such as changing temperature and humidity.
Nevertheless, the use of electrical signals and devices and apparatus for switching and using such signals have traditionally been much more extensively used. As a result, electromechanical switch construction and packaging has been standarized to the point that various families of such switches are relatively well defined in terms of switch housing configuration, actuator arrangements, mechanical operating characteristics, mounting hole spacing, etc.
Electromechanical switch design has also been refined to the point that the switches of any particular class can be relied upon as having quite precise and repeatable switching characteristics. One of the mechanical characteristics associated with precision switching is low travel of the switching element between actuated and unactuated states. This characteristic is commonly achieved through the use of an over center snap acting mechanism, of which a number of well developed designs are now in existence.
With the increasing trend toward adopting control systems using light signals and toward replacing existing electromechanical control systems and components in some applications with corresponding optomechanical control systems and components has come an increasing need for optomechanical switches which duplicate as nearly as possible the form, fit and mechanical characteristics of existing standard electromechanical switches. With this as an objective, many previous snap acting mechanism designs have been applied to optomechanical switches.
For example, U.S. Pat. No. 4,170,731 issued to M.J. Howell, et al. on Oct. 9, 1979 discloses a control module for blocking or permitting the passage of light between opposing ends of a pair of optical fiber bundles. The end portions of the optical fiber bundles are held in coaxial alignment by a switch body having a cavity therein which accommodates a generally L-shaped spring formed of a flat strip of resilient material. The end of the long leg of the L is fixed in the body so that in unactuated state the long leg is substantially parallel with the axis of the fiber bundles and the short leg of the L projects toward a gap between the ends of the bundles. An actuator plunger permits the long leg of the L to be deflected so as to bring the short leg of the L into the gap to block the passage of light between the ends of the bundles. The long leg of the L is also formed with a dimple which results in an "oil canning" action of the spring as the plunger is depressed to provide snap action. Because the short leg of the L swings through an arc in a plane containing the axis of the fiber bundles, a relatively wide gap between the ends of the bundles is required to provide clearance for movement of the short leg of the L.
U.S. Pat. No. 4,196,348 issued to N. Iwakiri, et al. on Apr. 1, 1980 discloses a contactless snap action photoelectric switch in which the passage of light between a light emitting diode and a photo electric device is selectively permitted or blocked by a light blocking portion of a shutter, the light blocking portion being carried on the end of an arm extending generally perpendicular to the direction of light transmission. The arm is held in tension by a bowed compression member lying generally in the plane of the arm to provide snap action of the shutter.
U.S. Pat. No. 4,223,217 issued to J.A. Bongard on Sept. 16, 1980 discloses a fiber optic electric switch comprising a fiber optic module which may be inserted in a standard limit switch enclosure, and which is designed so that motion of a conventional snap acting contactor mechanism is transferred to a slidable shutter which, in one position, is located in a gap between opposing ends of a pair of fiber optic cables. Opposite ends of the shutter are held between the ends of a pair of arms in a substantially parallel arm arrangement. One of the arms is L-shaped, with the end of the short leg of the L bearing against the contactor element and being effectively pivoted in the switch housing about a point substantially at the intersection of the long and short legs. The other arm of the parallel arm arrangement is cantilevered from the housing with the free end biasing the shutter toward the L-shaped arm.
British Patent No. 1,527,342 published on Oct. 4, 1978 discloses a plunger actuated snap acting switch which, in one embodiment, is configured to selectively interrupt the passage of light between a light emitting diode and a photo transistor. The snap acting mechanism basically comprises a leaf spring held in compression in the switch housing in a bowed configuration. The spring extends generally parallel with the direction of light transmission. The spring is formed with a folded back L-shaped extension of which the short leg of the L is positioned to be movable into the gap between the light emitting diode and photo transistor so that when the spring is actuated by the plunger to snap into its alternate position, the short leg of the L interrupts the transmission of light.
Of the foregoing prior art designs, only that of U.S. Pat. No. 4,223,217 is configured to simulate a standard electromechanical limit switch in form, fit and mechanical characteristics. However, this design suffers from being mechanically complex. The sliding shutter and parallel arm arrangement are likely to be susceptible to binding which would impair free movement required for precision operation, and are likely to be suspectible to mechanical wear and reduced life.
The applicant has provided an optomechanical switch design especially suited for use in a heavy duty limit switch, the movable light blocking shutter mechanism being of exceptionally simple design and arranged to permit a very narrow gap between opposing end faces of a pair of optical fibers so as to maximize light transmission between the end faces when so permitted by the shutter.